By the BBC's Brian Barron on Board USS Theodore Roosevelt in the Northern Arabian Sea

As the latest major US warship to arrive off the Pakistan coast, this nuclear-powered aircraft carrier has been assigned the "night shift" in the war.

That means its main task is to start catapulting F-14 and F-18 strike fighters on bombing missions against targets in Afghanistan just before midnight.

Those sorties in small clusters of planes continue throughout the night.

The "day" starts with wake-up and breakfast at about 1730

"These are intensely difficult missions," says Admiral Mark Fitzgerald, an aviator himself, who commands the Roosevelt battle group, one of three in the Arabian Sea.

The first problem is distance.

"The nearest targets could be at least 1,000 miles [1,600 kilometres] away - more if we are hitting Taleban positions in Northern Afghanistan.

"The flight crews are in the air seven or eight hours", says the Admiral.

Days reversed

"They come back tired and stiff and then they have to make a night landing on this aircraft carrier and that's never easy."

In an effort to ease the demands on the 5,500 men and women on the Roosevelt, the normal daily cycle has been reversed.

The "day" starts with wake-up and breakfast at about 1730.

Then comes the time to prepare the strike planes, load and arm the laser-guided bombs and missiles and fuel up the ASACS radar aircraft and tanker planes that will service the aerial armada.

The F-14s and F-18s will need mid-air refuelling at least four times during every night sortie.

"Lunch" on the Roosevelt is at around midnight, and dinner about five hours later.

Fatigue hazardous

These elaborate logistics, with the US navy carriers playing the main role in the aerial assault, are a reminder that the United States has not had much luck in persuading Muslim allies to make airbases available for its strike planes.

For that reason, air force heavy bombers B-1s, B-2s and B-52s have to fly their sorties either from Diego Garcia in the Indian Ocean or from their home bases in mainland America.

It is very clear that on the Roosevelt, fatigue is the main hazard.

There is stress but it's what I'd call the right kind of stress...Our duty is clear and there are no doubts about it

USS Roosevelt's resident psychologist

Everyone is working 12 to 15 hours a day. The officers often exceed even these hours, snatching sleep when they can.

Still, morale and motivation are high because everyone I met believes in the justness of the cause.

The resident psychologist on the Roosevelt, with the rank of commander, says the routine kind of tensions that crop up on a typically deployment are not being encountered.

"There is stress," he explains "but it's what I'd call the right kind of stress. We're all very focused. We know what we have to do. Our duty is clear and there are no doubts about it."

Safer than home

Even so, the commander is organising counselling sessions for those among the Roosevelt's crew who are acutely worried about their loved ones back home because of the anthrax alarm.

"The fact is we're safer out here on this ship than they are," says the commander.

Most of the crew I met prefer to remain anonymous.

In this conflict the US defence department has given individuals the right to choose for themselves whether to disclose their identities when talking to the media.

The unspoken fear is that given the terrorist attacks on America on 11 September, no one can rule out the families of US military personnel being targeted.

Potent player

In the last 24 hours, the Roosevelt played host to the commandant of the US Marine Corps, General James Jones.

He came by helicopter after visiting the 2,200 marines on board the amphibious carrier, the USS Pelilieu.

With their assault helicopters and harrier attack planes, they might be committed in any wider ground war.

But that seems weeks if not months away.

For the moment, nightly bombing sorties from the Roosevelt remain on of the most potent elements of the Pentagon's strategy.